skip cmake configure if cache is hit

.github/workflows/prototyping.yml

@@ -35,6 +35,7 @@ jobs:
         path: ~/.cabal/store
         key: prototyping-${{ runner.os }}-${{ matrix.agda }}
     - uses: actions/cache@v2
+      id: luau-ast-cache
       with:
         path: ./build
         key: prototyping-${{ runner.os }}-${{ hashFiles('Ast/**', 'Analysis/**', 'CLI/Ast.cpp', 'CLI/FileUtils.*')}}
@@ -59,11 +60,13 @@ jobs:
         ~/.cabal/bin/agda --compile PrettyPrinter.agda
         ~/.cabal/bin/agda --compile Interpreter.agda
     - name: cmake configure
+      if: steps.luau-ast-cache.cache-hit != 'true'
       run: |
         mkdir build
         cd build
         cmake build ../
     - name: cmake build luau-ast
+      if: steps.luau-ast-cache.cache-hit != 'true'
       run: |
         cmake --build ./build --target Luau.Ast.CLI
     - name: run tests